A. Field of the Invention
This invention relates generally to the field of telecommunication and the processes by which digital data is transmitted between computer systems over a telephone network or other communications link. The invention is particularly suitable for use in devices that support Integrated Services Digital Network (ISDN) digital telephone services or other serial communications.
B. Description of Related Art
The Point-to-Point Protocol (PPP) provides a standard method of encapsulating network layer protocol information over point-to-point links. The PPP also defines an extensible Link Control Protocol (LCP), and proposes a family of Network Control Protocols (NCPs) for establishing and configuring different network-layer protocols. The PPP is described in detail in a series of documents known as the Request For Comments, with which those of skill in the art are familiar. The Request For Comments (RFC) 1661, which is incorporated by reference herein, gives an informative overview of the PPP.
The initial deployment of the PPP has been over short local lines, leased lines, and plain-old-telephone-service (POTS) using modems. As new packet services and higher speed lines are introduced, PPP is easily deployed in these environments as well.
The PPP has three main components:
1. A procedure for encapsulating datagrams over serial links; PA1 2. A Link Control Protocol (LCP) for establishing, configuring, and testing the data-link connection; and PA1 3. A family of Network Control Protocols (NCPs) for establishing and configuring different network-layer protocols.
In order to establish communications over a point-to-point link, each end of the PPP link must first send LCP packets to configure the data link during the Link Establishment phase. After the link has been established, PPP provides for an optional Authentication phase before proceeding to the Network-Layer Protocol phase.
PPP encapsulation of data communications is possible when the data is transmitted over digital communication lines, such as ISDN lines. ISDN Basic Rate Service comprises two data channels (referred to as bearer channels or "B" channels), and a control channel known as the "D" channel. The ISDN D-channel can also be used for sending PPP packets when suitably framed, but is limited in bandwidth and often restricts communication links to a local switch. Since the ISDN B-channel is by definition a point-to-point link, PPP is well suited to use over ISDN lines.
The ISDN Primary Rate Interface may support many concurrent B-channel links. The PPP Link Control Protocol and Network Control Protocol mechanisms are particularly useful in this situation in reducing or eliminating hand configuration, and facilitating ease of communication between diverse implementations.
In order to accommodate ISDN data links over multiple channels simultaneously, a protocol known as PPP MultiLink or MP is used. The PPP MultiLink protocol is described in the Request For Comments 1717, which is incorporated by reference herein. A good discussion of the advantages of PPP Multilink can be found in an article authored by George E. Conant, entitled "Multilink PPP: One Big Virtual WAN Pipe", Data Communications, Sep. 21, 1995. In MP, the data stream, which consists of packets, is split up and inverse-multiplexed onto multiple channels (such as the two ISDN B channels), transmitted through the ISDN network, and then directed to the destination over multiple channels. The term "bundle", as used herein, is intended to mean a collection of links or logical connections that the are used for the communication session. In ISDN basic rate service, and where the two bearer channels are used for the session, the two bearer channels comprise a "bundle." At the destination, the data packet stream arriving in separate channels must be reconstituted or reconstructed after transiting the communication channels.
The above circumstance presents a challenge to the design of equipment for running PPP Multilink on a Primary Rate Interface server at the destination, since the server or termination point is interfacing with a large number of channels of incoming calls, two of which may together comprise a bundle. Heretofore, one approach as been that of fixed mapping, i.e., restricting all calls to a single server or gateway card. An alternative approach is time division multiplexing, but this approach has limited flexibility.
The present invention provides for a much more flexible solution. As described below, bundling information is shared between all of the termination units that receive the calls at the Primary Rate Interface. The present invention provides a method for controlling and coordinating bundles of data streams among multiple termination units, and the reconstitution of the session data at a designated termination unit for transmission of the call to the intended destination.
While the discussion below is primarily directed to an ISDN application, those of skill in the art will appreciate that the invention is applicable to any communication system in which a session arrives via multiple links at different termination units.